crabbydad

I have a 2000 Silverado with a 4.8L. At idle the alternator only puts out 12.5 volts, not enough to run the truck and recharge the battery. If I am stuck in traffic and do a lot of idling, when I get to my destination my battery is not charged enough to start the truck. I did a little experiment, when I stop at a light or in traffic, I depress the pedal just enough to bring the idle up another 100rpm or so, and the voltmeter in the truck goes up to 14.5 where it should be. The voltmeter in the truck is correct, I verified this with my meter. When I raise the rpm so that the alternator output is 14.5 I don't have any problems with the battery discharging. My question is if this is a bad regulator in my alternator and I need to replace my alternator or is there a problem with my computer? If I take it and have it checked at an auto parts store, I'm sure it will pass, but I think the problem is the internal regulator in the alternator. Anyone out there that had this problem or any experts who know?
thanks

tech2

irrc the alternator is ecm controlled.


check the alternator output at the large post on the alternator. if its 13.5 - 15 volts at the alternator...there may be voltage drops across the insulated and grd circuits.

chrenko59

Don't rule out a bad belt or tensioner... Sometimes the simple things are overlooked. If the belt is slipping even a little the alt. Will drop below needed rpm. You won't be able to tell by looking with a serpentine belt. If it is very old it would be worth the money to try a new belt, you would probability want to change it if you change the alt. Anyway. If that's not it, it will be the alt. I suggest you bring both home, try the belt and if that doesn't help you'll already have the alt. If it does you can take it back uninstalled.

crabbydad

I will check the voltage at the alternator. I was planning on replacing the serpentine as it is the original

Cowboycoupe

When I had similar trouble, I took the alternator off the vehicle, drove it down to an Autozone, and they put it on a test bench, analyzed it, and sold me the repair parts. )It needed a rectifier diode, and the regulator).

Another time, I had a similar problem, and discovered my fan belt (the old type), was slipping. New belt, problem solved.

Unless this is a computer problem, you should be able to solve this one by elimination.